This invention relates to a system (method and apparatus) for the location and treatment or removal of lesions, such as intracranial central nervous system (CNS) lesions, and more particularly for defining the location of lesions in a three-dimensional coordinate system with reference to a stereotactic guide ring used during surgery or treatment.
The integrated concept of the present invention has more general applications than the particular surgical procedure to be described for locating and removing a tumor in the brain. It may also be used for precisely locating adjuvant therapy. Also it can be used in other parts of the body for either surgical procedure or for adjuvant therapy. The system utilizes a stereotactic guide ring, as will be described by way of example for the removal of CNS lesions. There, as in other parts of the body, the removal could be carried out with a knife, a laser or concentrated gamma rays. Emphasis in the exemplary embodiment to removal of a CNS lesion is due only to the early success of the system for removing brain tumors.
In the past, the cure rate for malignant brain tumors has been virtually zero. This is partly due to the size to which the tumor must grow before its presence is diagnosed. If tumors can be detected while still very small in size, possibly 2 mm, they can be precisely located and removed by the surgical procedures described hereinafter. The amount of cancer material that might be left is so small that precisely administered adjuvant therapy, local irradiation, chemotherapy, immuno therapy, etc., may be satisfactory additional treatments.
The techniques that have been used for brain imaging in trying to determine the presence of a tumor are various. See Wm. H. Oldendorf, M.D., "The quest for an image of brain: A brief historial and technical review of brain imaging techniques," Neurology, 28:517-533, June, 1978. Of the various techniques, computerized tomography (CT) has a distinct advantage. Like other techniques, it is noninvasive, but unlike other techniques, it provides explicit two-dimensional images (sections) of the brain. To develop a three-dimensional image, it is necessary to provide a number of parallel CT scans (slices) over the volume of interest. CT scan instruments have been capable of imaging very accurately across 5-mm slices, and more recently across 1.7-mm slices. In other words, CT scanners have for some time been able to image very accurately thin cross sections of brain tissue in a two-dimensional (X-Y coordinate) display.
By using specially designed computer programs to analyze the digitized CT scan data, it should be possible to determine within a fraction of a millimeter the depth (Z coordinate) from the top of the head at which the tumor is located as well as the side-to-side (X coordinate) and front-to-back (Y coordinate) positions. The problem is how to use this information to locate the tumor with the same degree of accuracy during surgery as is possible in the CT scan. In the past, neurosurgeons have resorted to the technique of locating the tumor with reference to prominent cranial features, such as the locations of the sockets for the ears, eyes and nose. Obviously such "landmarks" are inadequate for the task of locating a tumor that may be less than 5-mm in diameter. So in practice, CT scan data has been very useful for diagnosis, but much less useful for surgery. This is particularly so because while CT scan data may be used to determine X and Y coordinates with accuracy, it is more difficult to determine the Z coordinate due to the lack of a precise base line for the first slice of the scan. A beam of light on the scalp, or calculation of the orbitomeatal line are not accurate enough for use in determining the Z coordinate of a very small lesion.
Continued improvement in CT resolution may soon lead to the localization of an intracranial tumor too small to be located and removed by conventional methods. This possibility led the inventors of the present invention to consider stereotactic methods of dealing with minute lesions since no surgical method had previously been available for approaching accurately such small lesions. A stereotactic system using a tissue expander is described by C. Hunter Shelden, et al., in an application Ser. No. 797,843, filed May 17, 1977, now U.S. Pat. No. 4,386,602 titled "Intracranial Surgical Operative Apparatus." Briefly, a stereotactic guide mechanism is clamped on the patient's head for holding a micromanipulator fixed relative to the cranium. The stereotactic guide mechanism is clamped to an extension of the operating table and so adjusted as to place the micromanipulator in a position to hold a guide for surgical instruments at an appropriate angle in space for entry of the cranium in a straight line to the lesion. The angle of entry is selected by the neurosurgeon based upon such factors as the size, shape and location of the lesion, and specific areas of vital brain function to be avoided.
Once the stereotactic guide mechanism is properly aligned for the angle of entry, the guide on the micromanipulator is used during surgery to advance the necessary instruments. First a scalp incision is made down to the bone, and a burr hole is made through the skull and enlarged as necessary. Next a dural incision is made and a small dilating probe is inserted which gradually displaces the brain tissue along the guided straight line to the depth of the target point (tumor). Other probes of successively larger diameter are inserted to expand the passageway sufficiently to allow easy insertion of an 8-mm tumorscope, a hollow probe with expandable tulip-like blades at the tip. After initial entry to the depth of the lesion, the blades at the tip are expanded by an inner tubular sleeve which, when moved distally, separates the blades to open the tip of the probe. When fully opened, the diameter of the circular opening across the tip is 6 mm. Opening the blades expands the surrounding tissue with sufficient stretch to prevent bleeding into the air-filled cavity created by the expanding blades. The tubular sleeve of the probe provides a 5-mm channel through which surgical instruments may be inserted, such as a stereo endoscope with xenon arc illumination, and a radiation tracer probe. A rotary extractor and other instruments necessary for the operation and removal of a tumor, or blood clot from a small intracerebral hemorrhage, are inserted through a lateral opening in the shaft of the scope. Thus, a micromanipulator for guiding the tactical instruments is, in turn, mounted on a stereotactic guide mechanism which accurately defines a passageway and maintains the straight line of approach at the desired angle of entry to the lesion which has been accurately located by the CT scan with reference to the cranium in three-dimensional coordinates.
The problem is to properly align the stereotactic guide mechanism so that the slide axis of the instrument guide passes through the center of the lesion, and to adjust the micromanipulator so that all of the probes, including the tumorscope with the expandable tip, can be inserted to just the precise depth. The angle and depth of entry cannot be accurately defined in a stereotactic guide mechanism with reference to cranial areas alone. At least not accurately enough for lesions of 5-mm or less.